What do I mean by test data?

If you are writing test case then you need input data for any kind of test. Tester may provide this input data at the time of executing the test cases or application may pick the required input data from the predefined data locations. The test data may be any kind of input to application, any kind of file that is loaded by the application or entries read from the database tables. It may be in any format like xml test data, system test data, SQL test data or stress test data.
Preparing proper test data is part of the test setup. Generally testers call it as test bed preparation. In test bed all software and hardware requirements are set using the predefined data values.
If you don’t have the systematic approach for building test data while writing and executing test cases then there are chances of missing some important test cases. Tester can’t justify any bug saying that test data was not available or was incomplete. It’s every tester’s responsibility to create his/her test data according to testing needs. Don’t even rely on the test data created by other tester or standard production test data, which might not have been updated for months! Always create fresh set of your own test data according to your test needs.
Sometime it’s not possible to create complete new set of test data for each and every build. In such cases you can use standard production data. But remember to add/insert your own data sets in this available database. One good way to design test data is use the existing sample test data or test bed and append your new test case data each time you get same module for testing. This way you can build comprehensive data set.